Researchers discover reason for skin discoloration in psoriasis

It's a common frustration: Your psoriasis flare-up finally goes away and in its place remains a patch of discolored skin.

Researchers at the Laboratory of Investigative Dermatology at The Rockefeller University have discovered a reason why – opening up opportunities for treatments for skin discoloration in psoriasis and skin conditions like eczema and acne.

Their findings were published in the Journal of Investigative Dermatology in 2013. They show that two immune system proteins that are known to cause the inflammation of psoriasis, the cytokines interleukin-17 (IL-17) and tumor necrosis factor alpha (TNF-alpha), also are to blame for skin discoloration.

The researchers found that IL-17 and TNF-alpha are interfering with the production of melanocytes – cells that produce the pigment that gives skin color. IL-17 and TNF suppress melanin, or pigment, production. Both proteins also promote the formation of melanocyte clusters.

"This was very surprising," said Claire Q. Wang, a research associate and the study's lead author, in a press release. "Melanocytes are believed to only replicate in the initial growth stage of melanocyte tumors, including melanomas. Here, in psoriasis, their numbers were doubled, sometimes tripled, but this was non-cancerous skin. This shows us that these cells are not as dormant in healthy individuals as scientists believe."

This finding helps scientists better understand what happens after a flare-up subsides.

"During a flare-up, there can be parts of skin with hypopigmentation — white spots," said Wang. "Then after it subsides, the spots turn dark. We think the increase in IL-17 and TNF induces this build-up of melanocytes, but prevents them from expressing the melanin until the inflammation settles down. Then the build-up is released, and the skin shows hyperpigmentation — dark spots."